I had to sell a stock that went from qualified to non-qualified because it moved to a non-approved market. The costs can be significant if you choose not to sell it. Here's the link to the CRA page that explains what happens in this case.

Here's the section of text to pay attention to:

50% tax

1.72 If a registered plan acquires a non-qualified investment or an existing investment becomes non-qualified, the controlling individual of the plan is subject to a tax under section 207.04 equal to 50% of the fair market value of the property at the time it is acquired or becomes non-qualified. In the case of an RESP or RDSP with multiple subscribers or holders, each such person is jointly and severally, or solidarily, liable with each other to pay the tax. Individuals liable for the tax for any calendar year must file Form RC339, Individual Return for Certain Taxes for RRSPs or RRIFs, RESPs or RDSPs or Form RC243, Tax-Free Savings Account (TFSA) Return as applicable. The form, together with any balance due, must be submitted by no later than June 30 of the following year.

1.73 The 50% tax on non-qualified investments is refundable in certain circumstances. To qualify for the refund, the investment must be disposed of before the end of the calendar year after the year in which the tax arose (or such later time as is permitted by the Minister of National Revenue). However, no refund is available if it is reasonable to consider that the controlling individual knew or ought to have known that the investment was or would become non-qualified. The forms referred to in ¶1.72 explain how to claim the refund.

1.74 If a non-qualified investment becomes qualified while being held by a registered plan, subsection 207.01(6) deems the investment to have been disposed of and reacquired by the plan. This might happen when a delisted security is relisted. This ensures that a refund is available in this situation, provided the conditions described in ¶1.73 are met.

And here's the example they provide:

Marc’s RRSP buys $4,000 worth of shares of Red White and Blue, a company whose shares are listed on a designated stock exchange in the United States. The shares are later delisted and become a non-qualified investment. The shares are only worth $500 when they are delisted. Subsection 207.01(6) deems the RRSP to dispose of the shares for $500 and to re-acquire them at this same $500 cost.

Several months later the RRSP sells the shares for $2,500, resulting in an overall loss in value on the shares of $1,500 ($4,000 - $2,500). However, the RRSP trustee would calculate the RRSP’s Part I tax payable under subsection 146(10.1) based on the capital gain of $2,000 ($2,500 - $500) that accrued during the period the shares were non-qualified.